This invention relates a method and a composition for separating plasma or serum from whole blood.
In clinical chemistry, the separation of serum or plasma from blood is of outstanding importance since, in practice, it is required to carry out the analysis of dissolved blood components without disturbance.
The normal and most conventional manner of separating serum or plasma from erythrocytes is centrifuging. However, especially in the case of using small amounts of sample, this gives rise to problems and the separation of supernatant and blood cake is not always simple so that, for this purpose, a whole series of adjuvants are to be found in the literature, for example Federal Republic of Germany Patent Specification No. 25 59 242.
The use of whole blood in the case of rapid diagnostic agents gives rise to special problems. Rapid diagnostics are reagent-containing, absorbent or swellable carriers, preferably filter paper, upon which a small amount, for example a droplet, of the liquid to be investigated is applied and in which, because of the preponderantly short period of reaction, a colour change takes place which is either evaluated visually or is measured remission photometrically. Since turbid or coloured solutions, such as blood, disturb the readings, attempts have, therefore, been made to make rapid diagnostics available for the direct use of whole blood. Thus, for example, mention may be made of the coating of test papers with semi-permeable membranes (see U.S. Pat. No. 3,092,465) and the use of swellable films into which only the dissolved components of the blood can penetrate but not the erythrocytes (see Federal Republic of Germany Patent Specification No. 15 98 153). These two methods are per se usable but only for tests for low molecular weight components of blood, for example glucose or urea; higher molecular weight components of the blood, for example lipids or substrates bound to serum protein, for example bilirubin, cannot be determined in this way because they are not able to penetrate into the film or to pass through the semipermeable membrane. Furthermore, suggestions have been made for covering diagnostic agents with membrane filters for separating off the blood cells (see Federal Republic of Germany Patent Specifications Nos. 22 22 951 and 29 22 958). A disadvantage of these diagnostic agents is that the blood can only penetrate through the membrane filter very slowly and in small amounts because the membrane is very easily blocked up and the reaction takes a correspondingly longer time. In contradistinction to the previously-mentioned diagnostic agents, which are already commercially available, "rapid tests" of the last-mentioned type have not yet been marketed.
Furthermore, from Federal Republic of Germany Patent Specifications Nos. 29 08 721 and 29 08 722, it is known that lymphocytes and leukocytes can be separated from blood when blood is filtered through a layer of synthetic resin fibres with an average fibre diameter of 5 to 20.mu. in the case of separating lymphocytes and of 3 to 10.mu. in the case of separating leukocytes. However, since the erythrocytes preponderantly pass through the filter with the plasma, these filters are not suitable for obtaining plasma. Furthermore, carbon fibres, glass fibres and metal fibres are mentioned purely speculatively.